Evolution der Gattung Echium auf den Kanarischen Inseln: vom Kraut zum Strauch zum Rosettenbaum

Abstract

The genus Echium is represented on the seven volcanic Canary islands by 24 closely related endemic species. As in other genera on the archipelago, the diversity in Echium is a result of rapid adaptive radiation during the last few million years. With molecular markers, the evolution of Echium on the Canary Islands can be traced back to a single colonisation event. In contrast to Echium species on the continent, most of the insular endemics are woody perennials. Some of the more spectacular species are giant rosette trees that flower only once and then die. The evolutionary diversification in Echium results from the drastic climatic changes in the past, from the climatic and edaphic diversity of habitats, and from genetic bottle­ neck events during the colonisation of newly formed volcanic islands. Today, the predominance of woodiness in endemic island species is explained by selection for longevity due to the scarcity of pollinators. The red-flowered E. wildpretii occurring in the volcanic Caldera of the highest mountain on Tenerife, Pico el Teide, is the most spectacular giant rosette tree of the archipelago and is pollinated by an endemic bird. From molecular studies the phylogenetic relationship among Echium species are well known. Their ecology, however, needs to be better explored in order to protect them from harmful consequences of habitat destruction and climatic change.